Divergent Waves Research Articles

Padé acoustoporoelasticity finite-difference simulation of elastic wave propagation in prestressed porous media

Abstract Acoustoelasticity has significant implications in seismic exploration, enabling the inference of geological structures and the properties of oil and gas reservoirs through rock physical acoustoelastic parameters, as well as elucidating the propagation of elastic waves in subsurface rocks. In traditional acoustoporoelastic numerical simulations, third-order elastic constants are derived from the Taylor expansion of the strain energy function. However, under conditions of high effective stress, the Taylor approximation can lead to divergent elastic wave velocities. To address this limitation, we propose employing the Padé approximation for the expansion of the strain energy function, as it provides superior accuracy compared to the Taylor approximation. By calibrating the Padécoefficients using experimental data for various rock types, the resultant acoustoelastic constants exhibit a reasonable theoretical limit on elastic wave velocities as effective stress increases. This method allows for a more precise characterization of velocity variations with stress, especially under high-pressure conditions. The acoustoporoelasticity numerical simulation is mainly limited to the 2D cases, so we consider confining prestressed mode in the 3D cases.

Influence of Regional Sea Ice Loss on the Arctic Stratospheric Polar Vortex

AbstractBased on multi‐model large‐ensemble experiments provided by Polar Amplification Model Intercomparison Project (PAMIP), we investigate the influence of the projected sea ice loss in Barents‐Kara Seas (BKS) and Sea of Okhotsk (SOK) on the Arctic stratospheric polar vortex (SPV). Results show that future BKS sea ice reduction leads to a weakened SPV during November‐February by enhancing the upward‐propagating planetary wave 1, which is more pronounced during Quasi‐Biennial Oscillation (QBO) easterly than westerly phase. Through weakening the upward‐propagating planetary wave 2, future SOK sea ice reduction is favorable for a strengthened SPV during January‐April. Inter‐model spread in the magnitudes of SPV responses to BKS sea ice reduction can be largely explained by the divergent planetary wave responses, but less so for SOK sea ice reduction. Results from a linearized baroclinic model further validate the importance of the planetary‐scale wave responses in explaining the differing SPV responses to sea‐ice loss over the two regions.

THE POST PANDEMIC CHALLENGES AND ECONOMIC RECOVERY OF SOUTH ASIAN NATIONS

The global economic recovery is facing a major challenge amid pressures such as new divergent waves of covid-19 disease outbreaks, continuing labor force challenges, persistent supply chain challenges and rising inflation. South Asian countries have maintained the pace of their economic recovery amid robust remittances and broadly supportive policy stances. Estimated at 7.4 percent in 2021, Asia's GDP is expected to expand at an average pace of 5.9 percent in 2022. However, South Asia's economic recovery is still weak and uneven. Fiscal policy remains highly restrictive, making it more challenging to a sustained recovery in economic activity and increase employment. As far as India is concerned, economic recovery is on a solid path amid a rapid vaccine easing social restrictions and supportive fiscal stance.

Illumination system contributing zooming function to lensless digital holographic microscope by using lightguide incorporated with volume holographic optical elements

Illumination systems play a crucial role in determining the image quality of lens- less images. In this paper, we propose an illumination system that uses a light guide with a volume holographic optical element (VHOE) and apply it to a lensless digital holographic microscope (DHM). The light guide has an in-coupler that is maturely developed for AR/MR applications. A VHOE serves as an in-coupler and directs the laser light into the guiding mode. Unlike the conventional light guide in the AR/MR application, the out-coupler is changed to a functional VHOE to diffract a divergent spherical wave. Through clever arrangement, the interference fringe caught by the CMOS image sensor can be used to retrieve the tested image. By controlling the focusing point of the diffracted spherical wave, the field of view (FOV) and the resolution can be adjusted. We have demonstrated the use of different VHOEs to perform different FOV and image resolutions. Thus, a zoomable-compact lensless DHM with holographic light guide technology is achievable.

In situ calibration of shear ratio for quadriwave lateral shearing interferometry using double-slit interference.

A new method, to the best of our knowledge, based on double-slit (DS) interference is proposed to accurately estimate the shear ratio of the system, with plane wave or spherical wave incidence. Existing shear ratio calibration methods, designed primarily for lateral shearing interferometry (LSI) with plane wave incidence, are not applicable to LSIs directly testing divergent or convergent spherical waves. Equations for calculating the shear ratio using the fringe spacing of the DS interferogram and the NA of the incident spherical wave are derived in this paper. The simulation result shows that the relative error of the shear ratio value is about 0.3%, when the shear ratio is 0.1. In the experiment, the quadriwave LSI is designed with a plug-in feature. The shear ratio at integer multiples of 1/6 Talbot distance from the modified Hartmann mask was calibrated using a DS, and the results were in good agreement with theoretical values, confirming the accuracy of the method. Subsequently, with the assistance of an inductance micrometer, the shear ratio was calibrated at intervals of 0.5mm, and the results closely matched the theoretical variation of the shear ratio caused by displacement, confirming the high precision of the method.

Hydrodynamic performance and wake study of an UUV sailing near the free surface

In this study, the SUBOFF UUV is numerically modelled in order to investigate the hydrodynamic features and effects of submerged navigation near the free surface. At various speeds and depths below the surface, the hydrodynamic behaviors of the SUBOFF UUV are examined. From the CFD results, we can deduce that submergence depth significantly affects total resistance of SUBOFF navigation nearby free surface. Because the Kelvin wake of SUBOFF creates wave-making resistance when approaching the open surface head-on, the fraction of pressure difference resistance becomes dramatically with an increase in Fr. The principle of superposition of the divergent wave system and the transverse wave system gradually reveals the divergent wave system as Fr grows larger. The wave making energy is greater, and the UUV needs more power to overcome the wave making resistance.

Use of the dilated electron propagator in conjunction with the modified smooth exterior scaling method to characterize 2S Be+ (1s−1), 2S Ne+ (1s−1) Auger and 2P Be− shape resonances

The modified smooth exterior scaling (MSES) method is an efficient method to impose outgoing boundary conditions in electron–atom or electron–molecule scatterings.

The reverse prediction of the ship principal dimensions based on the Kelvin ship waves

This study examines the impact of the ship’s principal dimensions on the steady waves generated by the ship, and practical approaches are subsequently proposed to reverse-predict the ship’s length, width, draught, and related parameters. The ship length Ls and the related Froude number Fr=Vs/gLs are found to relate with the quasi-period of the divergent wave amplitude function. The ship length can be predicted within an accuracy of ±5% overall based on the two-point wake model considered here. The effects of the ship width and the ship draught are different, and a practical method is proposed here to predict the ship width and the ship draught based on the simplification of the Hogner theory. A noteworthy discovery of this research is that the hull form details have a more pronounced impact on the trough of the divergent waves compared to the transverse waves and the peaks of the divergent waves.

Wave resistance of a ship moving in a lead between rigid ice sheets of finite thickness

This paper presents a combined theoretical and numerical analysis of a ship traveling in open water between rigid ice sheets of finite thickness with the objective to understand how the modeled ice influences the wave resistance and ship wave pattern. The first part of the analysis uses a mathematical model to evaluate the wave resistance in deep-water channels (or an ice sheet that reaches the sea floor). The model is able to separate the contributions of the transverse and divergent waves to the total wave resistance. Significant influence of both the ship speed and channel width is observed to both increase and decrease the wave resistance relative to the open water condition by as much as 50%. The second part of the analysis uses high-resolution computational fluid dynamics (CFD) on a contemporary ship that is traveling between two rigid ice sheets with finite thickness. The CFD simulations identify the critical ice thickness that corresponds to the condition in which the ice sheets function nearly as channel walls. It is found that the effect on the wave resistance is noticeable when the ice is 5% of the fundamental wavelength, and when the ice sheets are thicker than 20% of the fundamental wavelength, the resistance change due to the plates is nearly that of channel walls.

Behaviour of natural myocardial shear waves in children and adolescents: determinants and reproducibility

Abstract Funding Acknowledgements Type of funding sources: Private grant(s) and/or Sponsorship. Main funding source(s): Egyptian ministry of higher education and research Background Ultrafast echocardiography allows the direct non-invasive assessment myocardial shear waves (SW). These waves are naturally generated after mitral valve closure (MVC) and aortic valve closure (AVC) and their propagation velocities has been found to be linked to myocardial stiffness (MS) in adults. However, little experience exist regarding behaviour of such waves in children and normal values of SW velocities in children are lacking. Purpose This study aimed at setting up a reference range for SW velocities in paediatrics, determining influencing factors and exploring the reproducibility of their measurements in children. Methods One hundred-four healthy children (mean age 10 ±4 years old; range 2–18 years) were recruited. Participants were scanned with a research ultrasound scanner using divergent waves to yield a high frame rate of 1580 ±113 Hz. Parasternal long axis views (PLAX) were recorded for offline analysis. An anatomical M-mode was drawn along interventricular septum to visualize the propagation of shear waves after both MVC and AVC. Tissue Doppler acceleration maps were extracted and SW velocities were measured semi-automatically as the spatiotemporal slope of these waves (figure 1). Intra-class correlation coefficient (ICC) (2-way mixed model, absolute agreement between single measures) was used to check the reproducibility of these measurements among three raters. Results SW propagation velocities showed an association with clinical variables ; age (Figure2), body mass index (BMI) and body surface area (BSA). In addition, SW speeds showed association with local cardiac factors; ventricular septal thickness, LV mass and left ventricular end-systolic (LVESV) & end-diastolic volumes (LVEDV). Using a multivariate model; predictors of SW velocities after MVC are: age and LV mass (R2=0.59), while predictors of SW after AVC are: age, LV mass and LV volumes (R2= 0.33). In twenty-five randomly selected participants, moderate to good inter-observer reliability were noted among the three observers (ICC 0.84 [CI 0.70 to 0.92] after MVC, and ICC 0.83 [CI 0.69 to 0.92] after AVC). Conclusions Naturally occurring myocardial shear waves in children can easily be measured with acceptable reproducibility. Values are lower than in adults. SW velocities in children showed clear dependency on age, presumably due to growing heart size and increased myocardial muscle mass.

Experimental and numerical study on wave characteristics by a moving submerged body in a two-layer fluid

Waves induced by an immersed moving body in a two-layer fluid were studied experimentally and numerically. Unmixed fluids (water and cooking oil) were used as the two-layer fluid. A submerged body was manufactured to move with a wire loop system connected to the motor. The measured data were compared with numerical results and theoretical solutions. Numerical calculations were performed using the computational fluid dynamics (CFD) program. The characteristics of the generated waves, such as wave patterns and wavelengths, were qualitatively similar to the numerical results and theoretical values. Of the two wave propagation modes in a two-layer fluid, the baroclinic mode was dominant when the immersed body moved at a low speed. In contrast, the barotropic mode became more prominent as the body velocity increased. Based on these characteristics, transverse waves dominated when the velocity of the body was low, and divergent waves became more distinct as the velocity increased. In addition, the fluid depth and the location of a submerged body can affect the characteristics of the wave patterns.

Comparison of efficacy of platelet-rich plasma and extracorporeal shock wave for the treatment of chronic insertional Achilles tendinopathy

To compare clinical efficacy of platelet-rich plasma (PRP) and extracorporeal shock wave in treating chronic insertional Achilles tendinopathy. From February 2019 to August 2021, 42 patients with chronic insertional Achilles tendinopathy were selected and divided into PRP group(20 patients, 28 feet) and shock wave group (22 patients, 29 feet). In PRP group, there were 12 males and 8 females, aged 47.00(28.00, 50.75) years old, and the courses of disease ranged 7.00(6.00, 7.00) months;PRP injection was performed in the Achilles tendon stop area of the affected side. In shock wave group, there were 16 males and 6 females, aged 42.00(35.75, 47.25) years old;and the courses of disease was 7.00(6.00, 8.00) months;shock wave was performed in Achilles tendon stop area of the affected side and triceps surae area. Visual analogue scale (VAS) and Victorian Institute of Sport Assessment-Achilles (VISA-A) were applied to evaluate clnical effect before treatment, 1, 3 and 6 months after treatment, and satisfaction of patients was investigated. VAS and VISA-A score in both groups were significantly improved at 1, 3 and 6 months after treatment than before treatment (P<0.05), VAS and VISA-A score in PRP group at 6 months after treatment were significantly higher than those at 1 and 3 months after treatment, and VAS and VISA-A score in shock wave group were lower than those at 1 and 3 months after treatment (P<0.05). There was no significant difference in VAS and VISA-A score between two groups before treatment, 1 and 3 months after treatment(P>0.05), while VAS and VISA-A score in PRP group were better than those in shock wave group at 6 months after treatment(P<0.05), and the satisfaction survey in PRP group was better than that in shock wave group(P<0.05). PRP injection has a good clinical effect on chronic insertional Achilles tendinopathy with high patient satisfaction, and medium-and long-term effect of PRP injection for the treatment of chronic insertional Achilles tendinopathy is better than that of extracorporeal divergent shock wave.

Deletion of Cryab increases the vulnerability of mice to the addiction-like effects of the cannabinoid JWH-018 via upregulation of striatal NF-κB expression.

Synthetic cannabinoids have exhibited unpredictable abuse liabilities, especially self-administration (SA) responses in normal rodent models, despite seemingly inducing addiction-like effects in humans. Thus, an efficient pre-clinical model must be developed to determine cannabinoid abuse potential in animals and describe the mechanism that may mediate cannabinoid sensitivity. The Cryab knockout (KO) mice were recently discovered to be potentially sensitive to the addictive effects of psychoactive drugs. Herein, we examined the responses of Cryab KO mice to JWH-018 using SA, conditioned place preference, and electroencephalography. Additionally, the effects of repeated JWH-018 exposure on endocannabinoid- and dopamine-related genes in various addiction-associated brain regions were examined, along with protein expressions involving neuroinflammation and synaptic plasticity. Cryab KO mice exhibited greater cannabinoid-induced SA responses and place preference, along with divergent gamma wave alterations, compared to wild-type (WT) mice, implying their higher sensitivity to cannabinoids. Endocannabinoid- or dopamine-related mRNA expressions and accumbal dopamine concentrations after repeated JWH-018 exposure were not significantly different between the WT and Cryab KO mice. Further analyses revealed that repeated JWH-018 administration led to possibly greater neuroinflammation in Cryab KO mice, which may arise from upregulated NF-κB, accompanied by higher expressions of synaptic plasticity markers, which might have contributed to the development of cannabinoid addiction-related behavior in Cryab KO mice. These findings signify that increased neuroinflammation via NF-κB may mediate the enhanced addiction-like responses of Cryab KO mice to cannabinoids. Altogether, Cryab KO mice may be a potential model for cannabinoid abuse susceptibility.

The near-field wave interference of the steadily advancing monohull ships

An extension of the Neumann–Michell theory is given here — a more practical and efficient numerical approach is proposed , which only relates with the flow potential (instead of the related derivatives) and the related coefficients do not need to be updated repetitively during the iterative computations. A practical method is subsequently proposed to decompose the ship waves into the local, transverse or divergent wave components. The near-field ship waves along the ship hull and its effects of the wave interference on the wavelength, the wave drag and the hydrodynamic pressure are then considered. Clear relations between the near-field wavelength of the transverse or divergent ship waves and the Froude number are found, and the unfavorable or favorable interference relations in the near-field are given, which can predict the peaks or valleys of the wave drag more reasonable than the traditional far-field wave interference relations. Moreover, the effects of the transverse wave interference in the near-field is found more important than it conventionally believed, and it could be partially cancelled out by the wave interference of the divergent ship waves around the ship hull.

The wave interference and the wave drag of a leader–follower ship fleet

The wave interference and the corresponding effects on the wave drag of the leader–follower ship fleet are researched here, via a 4-point model and the Neumann-Michell potential flow computation. A simple analytical relation of the dominant wake angle is given, which considers both the wave interferences between the ship bow and the stern, and the wave interferences between the leader ship and the follower ship. Moreover, a simple relation of the destructive interference region (where the wave drag of the follower ship decreases) for the wave drag is given based on the research on the effects of the ship distance ℓ2 and the Froude number F on the wave drag of the leader ship or the follower ship. An interesting finding is that the destructive interference relation is invalid at low Froude numbers or very high Froude numbers, since the constructive interference of the divergent waves is apparent at low Froude numbers and the transverse waves is relatively small at high Froude numbers. These findings can be used to decrease the wave drag of ship fleets or ship formations.

Field measurement and analysis of ship generated waves in Hooghly river, India

Vessel movements in restricted waterways disturb the natural flow field and generate waves that create complex hydrodynamics. It is difficult to understand the general characteristics of ship-generated waves in restricted channels due to non-linearity and local bathymetry. A field study on the Hooghly river was conducted to assess and analyse the ship-generated primary and secondary waves. This paper investigated the wake signal from the field survey employing time-frequency analysis (short-term Fourier transform). The spectrogram study identified the primary and secondary waves from the wake signal. In comparison with the linear dispersion curve, the time-frequency study helps identify the divergent and transverse waves from the wave signal. The spectrogram study helps understand the influence of non-linearity from ship waves with increasing velocity. The energy content on the different components of the ship waves revealed the erosive potential of the waves. The measured primary and secondary waves were compared with the existing empirical relations, but satisfactory results were not obtained. Hence, a new empirical relationship between the primary and secondary waves has been obtained based on understanding the physical processes from the analysis of field data.

Cavitation bubble collapse and rebound in water: Influence of phase transitions

The influence of the mass transfer across the bubble surface due to evaporation and condensation on the cavitation (vapor) bubble collapse and rebound in water under room conditions has been studied. The bubble is spherical with an initial radius of 1.92mm. The dynamics of the vapor in the bubble and the surrounding liquid is governed by the gas dynamics equations. The effects of the liquid viscosity and heat conductivity of both fluids are taken into account. The liquid and vapor states are mainly described by the known wide-range equations by Nigmatulin and Bolotnova. The mass transfer is governed by the accommodation coefficient αac in the Hertz–Knudsen–Langmuir formula. It has been found that at αac in the range 0.001−0.075 the vapor in the bubble is homobaric at collapse. As αac increases in the range αac>0.075, an isentropic compression wave convergent to the bubble center is formed in the bubble. At focusing of this wave at the bubble center, a divergent (reflected from the center) isentropic compression wave occurs. With rising αac the intensities of these convergent and divergent waves increase. The divergent wave partially penetrates to the liquid in the form of an isentropic divergent wave. With growing αac the penetrated wave becomes steeper. At αac≈0.25 the divergent isentropic wave in the bubble transforms into a shock wave during its propagation to the bubble surface. This shock wave partially penetrates to the liquid in the form of a divergent shock wave. At small αac the outgoing pulse in liquid is shockless. Starting with αac≈0.03, it becomes discontinuous. In the range 0.03≤αac≤0.12 the shock pulse results from only large pressure gradients in the liquid in the vicinity of the bubble at the beginning of rebound. In the range 0.12<αac<0.25 the discontinuous outgoing pulse is formed from the divergent isentropic compression wave arisen in liquid as a result of partial escape of the isentropic wave out of the bubble. At αac>0.25 the shock pulse is formed directly on the bubbles surface as a result of the partial penetration of the divergent shock wave from the bubble to liquid. The obtained numerical results are in good agreement with available numerical and experimental data.

Ship’s Wake on a Finite Water Depth in the Presence of a Shear Flow

The ship’s wake in the presence of a shear flow of constant vorticity at a finite water depth is investigated by expanding the Whitham-Lighthill kinematic theory. It has been established that the structure of a wave ship wake radically depends on Froude number Fr (in terms of water depth) and especially on the critical Froude number Frcr, which depends on the magnitude and direction of the shear flow. At its subcritical values Fr&lt;Frcr two types of waves are presented: long transverse and short divergent waves inside the wedge area with an angle depending on Fr For the supercritical range Fr&gt;Frcr only divergent waves are presented inside the wake region. Critical Froude number Frcr is variable and mostly depends on collinear with the ship path component of the shear flow: it decreases with the unidirectional shear flow and increases on the counter shear current. The wedge angle of the ship wake expands with an increase in the unidirectional shear flow and narrows in the oncoming flow in the subcritical mode of the ship’s motion Fr&lt;Frcr. Wake angle decreased with Froude number for Fr&gt;Frcr and only divergent waves with the crests almost collinear with ship path are finally presented in the narrow ship wake. For a critical value of the Froude number Fr=Frcr, the ship’s wake has a total wedge angle of 180° with waves directed parallel to the ship’s motion. The presence of a shear flow crossing the path of the ship gives a strong asymmetry to the wake. An increase in the perpendicular shear flow leads to an increase in the difference between the angles of the wake arms.

Attenuation and inflection of initially planar shock wave generated by femtosecond laser pulse

Evolution of wavefront geometry during propagation and attenuation of initially planar shock waves generated by femtosecond laser pulses in aluminum is studied. We demonstrate that three stages of shock front inflection take place in consistent hydrodynamics and molecular dynamics simulations.During the first stage, the distance traveled by a near-planar wave DSW≲RL is smaller than the radius of heated laser spot RL. Wave attenuation is associated with one-dimensional plane (1D) rarefaction wave coming from the free surface. Such rarefaction wave shapes the shock wave to a 1D triangular pressure profile along direction normal to target surface with a shock front followed by an unloading tail. The second transitional stage starts after propagation of DSW∼RL, at which the unloading lateral waves begin to arrive to a symmetry axis of flow and initiate inflection of the initially planar shock front. Next at the third stage, the wavefront geometry is finally rounded and rapid attenuation of shock pressure begins at DSW≳RL.It is shown that such divergent shock wave cannot generate plastic deformations in aluminum shortly after propagation of DSW∼RL. Thus, we may estimate the maximal peening depth as a radius of focal spot, which sets an upper limit for the laser shock peening.The cessation of plastic deformation is caused by the fall of the shockwave amplitude below the elastic limit. In this case, the elastic-plastic wave transitions to a purely elastic mode of propagation. For large-sized light spots, this transition ends in the 1D mode of propagation.

Wake waves of a planing boat: An experimental model

The wake waves generated by the steady movement of a planing hull are analyzed by means of towing tank tests. Two sets of waves, including divergent and transverse waves, are identified and then analyzed. The wave period of the divergent waves is seen to decrease by the increase in speed of the vessel. These waves are seen to damp temporally. The mechanisms that lead to damping of the divergent wave were found to depend on the wave orbital Reynolds number in semi-planing regime, though that of in-planing regime is a function of the Reynolds number of the boat. The wake angle is seen to decrease with the increase in Froude number, the rate of which becomes relatively large in-planing regime. Transverse waves are captured through measurements, and it is shown that while their period is longer than those of the divergent waves, they are not noticeably damped. Throughout the spectral analysis, it is demonstrated that divergent waves reach a higher level of nonlinearity by the increase in Froude number and, hence, the wave energy is distributed over a boarder range of frequency. The height of the transverse wave is observed to become lower by the increase in speed, but as the towing speed increases, the probability density function curves of surface elevation deviate more and more from the Gaussian distribution.